Unprecedented cage-carbon to cage-boron NMe3 transfer in a monocarbon molybdenacarborane

Article abstract of DOI:10.1021/ic020091w

The reagent Li₂[7-NMe₃-nido-7-CB₁₀H₁₀] reacts with [Mo(CO)₃(NCMe)₃] in THF-NCMe (THF = tetrahydrofuran) to give a molybdenacarborane intermediate which, upon oxidation by CH₂=CHCH₂Br or I₂ and then addition of [N(PPh₃)₂]Cl, gives the salts [N(PPh₃)₂][2,2,2- (CO)₃-2-X-3-NMe₃- closo-2,1-MoCB₁₀H₁₀] (X = Br (1) or I (2)). During the reaction, the cage-bound NMe₃ substituent is transferred from the cage-carbon atom to an adjacent cage-boron atom, a feature established spectroscopically in 1 and 2, and by X-ray diffraction studies on several of their derivatives. When [Rh(NCMe)₃(η⁵-C₅ Me₅)][BF₄]₂ is used as the oxidizing agent, the trimetallic compound [2,2,2-(CO)₃-7-μ-H-2,7,11-{Rh₂ (μ-CO)(η⁵-C₅ Me₅)₂}-closo-2,1-MoCB₁₀H₉] (10) is formed, the NMe₃ group being lost. Reaction of 1 in CH₂Cl₂ with Tl[PF₆] in the presence of donor ligands L affords neutral zwitterionic compounds [2,2,2-(CO)₃-2-L-3- NMe₃-closo-2,1-MoCB₁₀H₁₀] for L = PPh₃ (4) or CNBu^t (5), and [2-Bu^tC≡CH-2,2-(CO)₂-3- NMe₃-closo-2,1-MoCB₁₀H₁₀] (6) when L = Bu^tC≡CH. When 1 is treated with CNBu^t and X₂, the metal center is oxidized, and in the products obtained, [2,2,2,2-(CNBu^t)₄-2-Br-3-X-closo-2,1- MoCB₁₀H₁₀] (X = Br (7), I (8)), the B-NMe₃ bond is replaced by B-X. In contrast, treatment of 2 with I₂ and cyclo-1,4-S₂(CH₂)₄ in CH₂Cl₂ results in oxidative substitution of the cluster and retention of the NMe₃ group, giving [2,2,2-(CO)₃-2-3-NMe₃-6- {cyclo-1,4-S₂ (CH₂)₄}-closo-2,1-MoCB₁₀H₉] (9). The unique structural features of the new compounds were confirmed by single-crystal X-ray diffraction studies upon 6, 7, 9 and 10.

Full text of DOI:10.1021/ic020091w

Inorg. Chem. 2002, 41, 3202−3211
Unprecedented Cage-Carbon to Cage-Boron NMe3 Transfer in a
Monocarbon Molybdenacarborane†
Shaowu Du, Jason A. Kautz, Thomas D. McGrath, and F. Gordon A. Stone*
Department of Chemistry & Biochemistry, Baylor UniVersity, Waco, Texas 76798-7348
Received February 1, 2002
The reagent Li2[7-NMe3-nido-7-CB H ] reacts with [Mo(CO)3(NCMe)3] in THF−NCMe (THF ) tetrahydrofuran) to
10 10
give a molybdenacarborane intermediate which, upon oxidation by CH dCHCH Br or I2 and then addition of [N(PPh ) ]-
2
2
3 2
Cl, gives the salts [N(PPh3)2][2,2,2-(CO)3-2-X-3-NMe3-closo-2,1-MoCB H ] (X) Br (1) or I (2)). During the reaction,
10 10
the cage-bound NMe3 substituent is transferred from the cage-carbon atom to an adjacent cage-boron atom, a
feature established spectroscopically in 1 and 2, and by X-ray diffraction studies on several of their derivatives.
When [Rh(NCMe)3(η5-C Me5)][BF ] is used as the oxidizing agent, the trimetallic compound [2,2,2-(CO)3-7-µ-H-
5
4 2
2,7,11-{Rh2(µ-CO)(η5-C Me5)2}-closo-2,1-MoCB H ] (10) is formed, the NMe3 group being lost. Reaction of 1 in
5
10 9
CH Cl2 with Tl[PF ] in the presence of donor ligands L affords neutral zwitterionic compounds [2,2,2-(CO)3-2-L-3-
2
6
t
t
NMe -closo-2,1-MoCB H ] for L ) PPh (4) or CNBu (5), and [2-BuCtCH-2,2-(CO)2-3-NMe -closo-2,1-MoCB H ]
3
10 10
3
3
10 10
t
t
(6) when L ) BuCtCH. When 1 is treated with CNBu and X , the metal center is oxidized, and in the products
2
t
obtained, [2,2,2,2-(CNBu)4-2-Br-3-X-closo-2,1-MoCB H ] (X ) Br (7), I (8)), the B−NMe3 bond is replaced by
10 10
B−X. In contrast, treatment of 2 with I2 and cyclo-1,4-S (CH ) in CH Cl2 results in oxidative substitution of the
2
2 4
2
cluster and retention of the NMe3 group, giving [2,2,2-(CO)3-2-I-3-NMe3-6-{cyclo-1,4-S (CH ) }-closo-2,1-MoCB H ]
2
2 4
10 9
(9). The unique structural features of the new compounds were confirmed by single-crystal X-ray diffraction studies
upon 6, 7, 9 and 10.
Introduction
respectively.2d,3 The potential of these amino-nido-carboranes
for synthesis has, however, been but little exploited. More-
over, recent work has revealed some subtle differences in
the nature of the products obtained in their reactions with
low-valent transition-metal compounds. Thus, whereas, for
Transition-metal complexes of the trianionic mono-
carbollide ligand [nido-7-CB10H11]3- had until recently
received relatively little attention compared with the wealth
of information available on the corresponding complexes of
the dicarbollide ligand [nido-7,8-C2B9H11]2- and its deriva-
tives.1 The carboranes 7-NR3-nido-7-CB10H12 (R ) H, alkyl)2
are also precursors to monocarbollide metal complexes,
affording species containing the C-amine and -amino ligands
[7-NR3-nido-7-CB10H10]2- and [7-NR2-nido-7-CB10H10]3-,
example, the carboranes 7-NR3-nido-7-CB10H12 (NR3
)
NMe3, NH2But, NMe2But) all react with [Ru3(CO)12] in
toluene at reflux temperatures to yield the cluster compounds
[1-NR3-2,2-(CO)2-7,11-(µ-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-
RuCB10H8],4 the nido-carboranes show some variation in
their reactivity with [RhCl(PPh3)3] for different groups R.5
In methanolic KOH solution, 7-NH3-nido-7-CB10H12 reacts
with [RhCl(PPh3)3] to give salts of [1-NH2-2,2-(PPh3)2-2-
* Author to whom correspondence should be addressed. E-mail:
gordon_stone@baylor.edu.
† The new compounds described in this paper are based on icosahedral
closo-1-carba-2-molybdenadodecaborane frameworks, and although all are
chiral, they here occur as racemates. The substituted boron vertices that
herein are numbered 3, 6, 7, and 11 could equally be labeled 6, 3, 11 and
7, respectively. In each case, the former is used, in accordance with IUPAC
convention.
(2) (a) Hyatt, D. E.; Owen, D. A.; Todd, L. J. Inorg. Chem. 1966, 5,
1749. (b) Knoth, W. H. J. Am. Chem. Soc. 1967, 89, 1274. (c) Hyatt,
D. E.; Scholer, F. R.; Todd, L. J.; Warner, J. L. Inorg. Chem. 1967,
6, 2229. (d) Knoth, W. H. Inorg. Chem. 1971, 10, 598. (e) Jeffery, J.
C.; Jelliss, P. A.; Karban, J.; Lebedev, V.; Stone, F. G. A. J. Chem.
Soc., Dalton Trans. 1997, 1219.
(3) Hyatt, D. E.; Little, J. L.; Moran, J. T.; Scholer, F. R.; Todd, L. J. J.
Am. Chem. Soc. 1967, 89, 3342. Knoth, W. H. J. Am. Chem. Soc.
1967, 89, 3342.
(1) Grimes, R. N. In ComprehensiVe Organometallic Chemistry; Wilkin-
son, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon Press: Oxford,
U.K., 1982; Vol. 1, Section 5.5. Grimes, R. N. In ComprehensiVe
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon Press: Oxford, U.K., 1995; Vol. 1, Chapter 9.
Grimes, R. N. Coord. Chem. ReV. 2000, 200-202, 773.
(4) Lebedev, V. N.; Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.
Organometallics 1996, 15, 1669.
3202 Inorganic Chemistry, Vol. 41, No. 12, 2002
10.1021/ic020091w CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/18/2002

Cage-Carbon to Cage-Boron NMe3 Transfer
Scheme 1
H-closo-2,1-RhCB10H10]-, of which the [Bun N]+ salt is con-
with that work, we attempted to prepare another analogue
of the latter anion, namely the dianionic molybdenacarborane
[2,2,2-(CO)3-1-NMe3-closo-2,1-MoCB10H10]2-, with a view
to examining comparable reactivity. However, as we report
herein, this last species is very readily oxidized undergoing
an unprecedented cage-carbon to cage-boron transfer of the
NMe3 group. The nature and reactivity of the product is
discussed, as are some related reactions.
4
verted in refluxing methanol to the dimeric species [Bun N]-
4
[2,2′-µ-H-{1,2′-µ-NH2-2-PPh3-closo-2,1-RhCB10H10}2]-.5a In
contrast, the carborane 7-NMe3-nido-7-CB10H12 with the
same rhodium reagent in refluxing methanol yields pri-
marily 18-electron [1-NMe3-2,7-(PPh3)2-2-H-2-Cl-closo-2,1-
RhCB10H9], along with 16-electron [1-NMe3-2-PPh3-2-
Cl-closo-2,1-RhCB10H10].5b Moreover, 7-NH2But-nido-7-
CB10H12 reacts with [RhX(PPh3)3] (X ) Cl or Br) in
refluxing toluene to give 16-electron [1-NH2But-2-PPh3-2-
X-closo-2,1-RhCB10H10] as the only products.5c
These differences in reactivity of the carboranes 7-NR3-
nido-7-CB10H12 toward [RhX(PPh3)3] have led us to explore
their behavior in reactions with other transition-metal
systems. We have recently reported6 the synthesis of the
monoanionic molybdenacarborane salt [N(PPh3)2][1,2-µ-
NHBut-2,2,2-(CO)3-closo-2,1-MoCB10H10], which contains
a novel intramolecular NHBut bridge between molybdenum
and the cage-carbon atom. This species is obtained upon
oxidation of trianionic [1-NHBut-2,2,2-(CO)3-closo-2,1-
MoCB10H10]3-. The latter was targeted for synthesis because
of its isolobal relationship with the ubiquitous dicarbollide
dianion [3,3,3-(CO)3-closo-3,1,2-MoC2B9H11]2-.7 In concert
Results and Discussion
The molybdenum dicarbollide dianion [3,3,3-(CO)3-closo-
3,1,2-MoC2B9H11]2- has previously been used to prepare
[3-(η3-C3H5)-3,3-(CO)2-closo-3,1,2-MoC2B9H11]- by reaction
with CH2dCHCH2Br.8 Employing an ostensibly parallel
monocarbollide system, we planned to treat a THF solu-
tion of [7-NMe3-nido-7-CB10H10]2- with [Mo(CO)3(NCMe)3]
in NCMe, in the expectation of generating in situ the
monocarbollide species [2,2,2-(CO)3-1-NMe3-closo-2,1-
MoCB10H10]2-. However, the latter in reaction with CH2d
CHCH2Br did not afford the anticipated anion [1-NMe3-2-
(η3-C3H5)-2,2-(CO)2-closo-2,1-MoCB10H10]-. Instead, the
product isolated following addition of [N(PPh3)2]Cl was
[N(PPh3)2][2-Br-2,2,2-(CO)3-3-NMe3-closo-2,1-MoCB10-
H10] (1; Scheme 1). In addition to oxidizing the molybdenum
center, the allyl bromide also serves as a bromide source.
Most significant, however, is that during the course of
reaction the NMe3 group that had been bonded to the cage-
carbon atom has transferred to an adjacent boron atom (BR)
(5) (a) Walker, J. A.; O’Con, C. A.; Zheng, L.; Knobler, C. B.; Hawthorne,
M. F. J. Chem. Soc., Chem. Commun. 1983, 803. (b) Chizhevsky, I.
T.; Pisareva, I. V.; Petrovskii, P. V.; Bregadze, V. I.; Dolgushin, F.
M.; Yanovsky, A. I.; Struchkov, Yu. T.; Hawthorne, M. F. Inorg.
Chem. 1996, 35, 1386. (c) Jeffery, J. C.; Lebedev, V. N.; Stone, F. G.
A. Inorg. Chem. 1996, 35, 2967.
(6) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. Inorg. Chem.
2001, 40, 6563.
in the CBBBB belt that ligates the molybdenum vertex.
(7) Hawthorne, M. F.; Young, D. C.; Andrews, T. D.; Howe, D. V.; Pilling,
R. L.; Pitts, A. D.; Reintjes, M.; Warren, L. F., Jr.; Wegner, P. A. J.
Am. Chem. Soc. 1968, 90, 879.
(8) Dossett, S. J.; Li, S.; Stone, F. G. A. J. Chem. Soc., Dalton Trans.
1993, 1585.
Inorganic Chemistry, Vol. 41, No. 12, 2002 3203

Du et al.
Table 1. Analytical and Physical Data
anal./%b
H
cmpd
color
red
yield/%
27
ν
max(CO)a/cm-1
C
N
[N(PPh3)2][2-Br-2,2,2-(CO)3-
3-NMe3-closo-2,1-MoCB10H10] (1)
[N(PPh3)2][2,2,2-(CO)3-2-I-3-NMe3-
closo-2,1-MoCB10H10] (2)
2013 s, 1933 s,
1896 s
2006 s, 1932 s,
1894 s
52.4 (52.3)
5.1 (5.0)
3.0 (2.8)
red
13
63
71
89
43
43
47
20
51.3 (51.0)
45.5 (45.4)
31.9 (31.9)
33.3 (34.0)
35.5 (35.1)
32.2 (32.0)
21.1 (21.5)
36.8 (36.9)
5.0 (5.2)
5.5 (5.2)
6.3 (6.2)
6.9 (6.9)
6.5 (6.4)
5.9 (5.9)
4.4 (4.3)
5.0 (5.0)
3.0 (2.5)c
2.3 (2.1)d
6.2 (6.2)
3.3 (3.3)
7.4 (7.8)
6.7 (6.9)d
2.4 (2.3)
[2,2,2-(CO)3-2-PPh3-3-NMe3-
closo-2,1-MoCB10H10] (4)
yellow
yellow
purple
orange
orange
red
2017 s, 1956 s,
1906 s
[2-CNBut-2,2,2-(CO)3-3-NMe3-
closo-2,1-MoCB10H10] (5)
2170 m,e 2038 s,
1985 s, 1930 s
2039 s, 1979 s
[2-ButCtCH-2,2-(CO)2-3-NMe3-
closo-2,1-MoCB10H10] (6)
[2,2,2,2-(CNBut)4-2,3-Br2-
2213 w,e 2184 se
2208 w,e 2181 se
closo-2,1-MoCB10H10] (7)
[2,2,2,2-(CNBut)4-2-Br-3-I-
closo-2,1-MoCB10H10] (8)
[2,2,2-(CO)3-2-I-3-NMe3-6-{cyclo-1,4-
S2(CH2)4}-closo-2,1-MoCB10H9] (9)
[2,2,2-(CO)3-7-µ-H-2,7,11-{Rh2(µ-CO)(η5-C5Me5)2}-
closo-2,1-MoCB10H9] (10)
2019 s, 1958 m,
1922 s
1998 s, 1939 m,
1826 m
brown
a
b
Measured in CH2Cl2; the broad medium-intensity band observed at ∼2500-2550 cm-1 in the spectra of all compounds is due to B-H absorptions.
c
d
e
Calculated values are given in parentheses. Cocrystallizes with 1 mol equiv of thf. Cocrystallizes with 0.5 mol equiv of CH2Cl2.
νmax(NtC).
Table 2. 1H, 13C, and 11B NMR Dataa
cmpd
1H/δb
13C/δc
11B/δd
8.3 (1B),* -2.0 (1B),
-3.8 (2B), -7.5 (1B),
1
7.69-7.25 (m, 30H, Ph), 3.06 (s, 9H, Me),
ca. 3.03 (sh, br s, 1H, cage CH)
246.5, 236.7, 229.9 (CO × 3),
134.1-126.8 (Ph),
67.4 (br, cage C), 57.7 (NMe3)
-8.4 (1B), -10.8 (1B),
-13.4 (1B), -16.8 (2B)
8.1 (1B),* -1.7 (1B),
2
4
7.68-7.25 (m, 30H, Ph),
3.24 (br s, 1H, cage CH),
3.06 (s, 9H, Me)
244.3, 234.6, 229.2 (CO × 3),
134.1-126.8 (Ph),
60.7 (br, cage C), 57.9 (NMe3)
-3.4 (2B), -7.1 (1B),
-9.3 (1B), -11.6 (1B),
-13.4 (1B), -16.6 (1B), -17.3 (1B)
11.4 (1B),* 2.8 (1B),
7.52-7.31 (m, 15H, Ph),
2.95 (s, 9H, Me),
1.63 (br s, 1H, cage CH)
235.7 (d, CO, J(PC) ) 8),
232.7 (d, CO, J(PC) ) 31),
230.3 (d, CO, J(PC) ) 33),
134.0-129.0 (Ph),
-3.1 (1B), -4.9 (2B),
-10.4 (1B), -11.7 (1B),
-14.1 (2B), -16.5 (1B)
57.4 (NMe3), 56.2 (br, cage C)
233.6, 229.8, 226.3 (CO × 3),
153.9 (t, CN, J(NC) ) 18),
60.8 (CMe3), 57.1 (NMe3),
54.7 (br, cage C), 30.3 (CMe3)
230.3, 225.0 (CO × 2),
5
6
3.00 (s, 9H, NMe3),
2.70 (br s, 1H, cage CH),
1.53 (s, 9H, But)
9.2 (1B)*, 1.3 (1B),
-3.8 (2B), -5.5 (1B),
-10.4 (1B), -12.4 (2B),
-15.3 (1B), -16.0 (1B)
12.6 (1B),* 2.5 (1B),
1.9 (1B), -2.2 (1B),
-3.5 (1B), -5.0 (1B),
-10.4 (1B), -12.4 (1B), -14.1 (2B)
10.1 (1B + 1B*), 4.4 (1B),
-3.3 (1B), -3.7 (1B),
-6.5 (3B), -15.7 (1B), -17.8 (1B)
11.1 (1B), 4.7 (1B),
-2.6 (2B), -5.7 (1B + 1B*),
ca. -6.1 (sh, 2B), -15.8 (2B)
7.7 (1B),* -2.4 (1B),
-4.3 (2B), -5.8 (2B),
-6.6 (1B),* -7.9 (1B),
-17.3 (1B), -18.2 (1B)
10.06 (br s, 1H, CtCH),
4.38 (br s, 1H, cage CH),
223.3 (CtCH), 175.0 (CtCBut),
57.6 (br, cage C), 56.9 (NMe3),
41.6 (CMe3), 31.3 (CMe3)
152.0 (br, CN), 62.2 (br, cage C),
58.2 (CMe3), 29.8 (CMe3)
2.45 (s, 9H, NMe3), 1.69 (s, 9H, But)
7
8
9
2.42 (br s, 1H, cage CH),
1.52 (s, 36H, But)
2.28 (br s, 1H, cage CH),
1.52 (s, 36H, But)
149.1 (br, CN), 62.7 (br, cage C),
58.5 (CMe3), 29.5 (CMe3)
3.89 (br m, 1H, CH2),
235.2, 224.3, 223.3 (CO × 3),
58.1 (NMe3), 57.8 (br, cage C),
42.3, 40.2, 27.3, 26.6 (CH2 × 4)
3.55-3.42 (m, 2H, CH2),
3.28-3.21 (m, 3H, CH2),
3.09 (s, 9H, NMe3),
ca. 3.08 (sh, br s, 1H, cage CH),
2.99-2.82 (m, 2H, CH2)
10
1.79, 1.76 (s × 2, 15H × 2, C5Me5 × 2),
251.1,e 225.1, 221.5 (CO × 3),
108.4 (d, C5Me5, J(RhC) ) 4),
106.0 (d, C5Me5, J(RhC) ) 6), 44.0 (br, cage C),
9.8, 9.3 (s × 2, Me × 2)
56.7 (1B, B-Rh),
29.3 (1B, B-HFRh, J(HB) ) 70),
-3.7 (1B), -5.6 (1B),
-6.8 (1B), -8.4 (1B), -10.9 (1B),
-11.8 (1B), -14.3 (1B), -18.3 (1B)
1.71 (br s, 1H, cage CH),
ca. -14.0 (vbr m, 1H, B-HFRh)
a
b
Chemical shifts (δ) in ppm, coupling constants (J) in hertz, measurements at ambient temperatures in CD2Cl2. Resonances for terminal BH protons
occur as broad unresolved signals in the range δ ca. -1 to +3. 1H-decoupled chemical shifts are positive to high frequency of SiMe4. 1H-decoupled
c
d
chemical shifts are positive to high frequency of BF3‚Et2O (external). Signals ascribed to more than one boron nucleus result from overlapping peaks and
e
do not indicate symmetry equivalence. Peaks marked with an asterisk are assigned to cage-boron nuclei bearing non-H substituents. Resonance due to
Rh-Rh-bridging CO not observed.
Spectroscopic data for compound 1 are given in Tables 1
and 2. Initially, however, the exact constitution of this species
was not clear. In addition to peaks due to an [N(PPh3)2]+
cation (confirmed by 31P{1H} NMR), the only significant
features of the 1H and 13C{1H} NMR spectra were resonances
attributable to the NMe3 substituent and three inequivalent
3204 Inorganic Chemistry, Vol. 41, No. 12, 2002

Cage-Carbon to Cage-Boron NMe3 Transfer
1
Mo-bound carbonyl ligands. Integration of the H NMR
spectrum indicated one cation per NMe3 group, implying the
molybdenacarborane to be monoanionic. Reasonably deduc-
ing the presence of a metal-bound bromide for overall
neutrality, compound 1 was initially incorrectly formulated
as [N(PPh3)2][2-Br-2,2,2-(CO)3-1-NMe3-closo-2,1-MoCB10H10],
with the NMe3 moiety assumed still to be attached to the
cage-carbon atom. A preliminary X-ray diffraction experi-
ment (see later) appeared to support this, as the anion
crystallizes with the NMe3 group lying across a crystallo-
graphic mirror plane and with the carborane ligand therefore
having apparent crystallographic mirror symmetry. However,
in the 11B{1H} NMR spectrum of 1, 10 separate resonances
are seen (some are coincident), of which one signal remained
a singlet in a fully coupled 11B spectrum. Both of these
features are consistent with a reduction in cluster symmetry
due to substitution at a boron vertex, and it was realized
that the available NMR data could better be explained if the
NMe3 substituent was bound to a cage-boron atom. Indeed,
the chemical shift of this boron atom (δ 8.3) is typical for
B-amine features in related systems.9 A shoulder observed
Figure 1. Structure of the anion of [N(PPh3)2][2-Br-2,2,2-(CO)3-3-NMe3-
closo-2,1-MoCB10H10] (1) showing the crystallographic labeling scheme.
In this and in Figures 2-5, thermal ellipsoids are drawn at the 40%
probability level, and hydrogen atoms are omitted for clarity except where
chemically important. Selected internuclear distances (Å) and angles
(deg): Mo-C(4) 1.799(12), Mo-C(2) 1.961(9), Mo-C(3) 2.010(8), Mo-
C(1) 2.31(4), Mo-B(4) 2.347(5), Mo-B(2) 2.452(8), Mo-B(3) 2.47(5),
Mo-Br 2.771(3), B(2)-N(1) 1.613(8), C(2)-O(2) 1.132(9), C(3)-O(3)
1.142(8), C(4)-O(4) 1.19(2); C(1)-Mo-Br 72.1(5), B(4)-Mo-Br
130.12(14), B(4)a-Mo-Br 85.20(14), B(2)-Mo-Br 104.94(6), B(3)-Mo-
Br 140.6(4), B(3)-B(2)-N(1) 125.6(9), N(1)-B(2)-B(6) 113.3(5),
N(1)-B(2)-C(1) 125.3(8), N(1)-B(2)-Mo 114.7(4). Symmetry code
(a): -x + 1, y, z.
1
at δ ∼3.03 in the H NMR spectrum of 1, which is almost
obscured by the signal for the methyl groups, may be
tentatively assigned as the cage CH resonance. This proposal
would also be consistent with the X-ray result with disorder
precluding the distinguishing of cage-boron versus cage-
carbon vertices. For the same reason, a distinction also could
not yet be made between the amine being attached to R or
Evidently, side reactions occur, but formation of other
identifiable molybdenacarborane products was not observed.
Unresolved at present is the manner by which the NMe3
group is transferred from carbon to boron in the formation
of 1 and 2. However, a plausible pathway is indicated in
Scheme 2, of which several steps have precedent.10 Oxidation
of the Mo0 dianion with allyl bromide or iodine would afford
the electronically unsaturated neutral MoII species [1-NMe3-
2,2,2-(CO)3-closo-2,1-MoCB10H10] (A) together with halide.
The latter would ligate the metal center to form the satu-
rated anionic complex [1-NMe3-2,2,2-(CO)3-2-X-closo-2,1-
MoCB10H10]- (B). In the next step affording C, iodine or
allyl bromide abstracts H- from a cage BHδ- vertex, thereby
creating a vacant site on a boron atom adjacent to the CNMe3
unit, causing the NMe3 group to migrate (D). The electron
deficient carbon center must then scavenge H- from other
species present in solution to yield the anions E, cage BH
groups being a likely source of hydride. This would perhaps
account for the formation of 1 and 2 in poor yield. The
removal of H- from B by iodine also occurs in the reaction
of the monoanion [2,2,2,2-(CO)4-closo-2,1-MoCB10H11]-
with iodine in THF which gives [2,2,2-(CO)3-2-I-7-
{O(CH2)4}-closo-2,1-MoCB10H10]-. In this process, the I-
formed by reduction of iodine again ligates the metal center,
but a THF molecule coordinates to a vacant site created on
the boron atom.10 It is noteworthy that in the synthesis of 1
and 2 the solvent is THF. Hence, it would in principle be
possible for a THF molecule to attach itself to the naked
boron in C obviating any need for NMe3 migration. That
this does not occur might suggest an intramolecular three-
â boron atoms in the CBBBB belt bonded to molybdenum.
Thus, it was not at this stage unambiguously established if
1 was the 3-NMe3 or the 7-NMe3 isomer.
The structure ultimately assigned for the anion of 1 is
shown in Figure 1. The site for the cage-carbon is based on
the results for closely related structures discussed later. A
molybdenum atom is ligated on one side by three carbonyls
and a bromide [Mo-Br 2.771(3) Å], and on the other side
by an 8-NMe3-nido-7-CB10H10 carborane in a conventional
pentahapto fashion. The B(2)-N(1) distance, at 1.613(8) Å,
is normal.
In seeking analogues of 1 which might afford a more
satisfactory crystallographic result, we found that the cor-
responding iodo compound [N(PPh3)2][2,2,2-(CO)3-2-I-3-
NMe3-closo-2,1-MoCB10H10] (2) could be obtained by using
I2 instead of CH2dCHCH2Br as oxidant in the reaction by
which compound 1 was formed. Data characterizing 2 are
given in Tables 1 and 2, showing this species to have very
similar spectroscopic properties to those of compound 1, as
would be expected. In particular, the broad proton resonance
diagnostic for the cage CH group is seen at δ 3.24 and is
now clearly distinguishable from the NMe3 proton resonance
at δ 3.06. The 11B{1H} NMR spectrum again reveals a
resonance at δ 8.1, assigned to the B-NMe3 group as it
remains a singlet in a fully coupled 11B NMR spectrum.
Unfortunately, 2 also failed to yield crystals suitable for an
accurate X-ray analysis. Isolated yields of 1 and 2 were low.
(9) Franken, A.; Du, S.; Jelliss, P. A.; Kautz, J. A.; Stone, F. G. A.
(10) Du, S.; Kautz, J. A.; McGrath, T. D.; Stone, F. G. A. J. Chem. Soc.,
Dalton Trans. 2001, 2791.
Organometallics 2001, 20, 1597.
Inorganic Chemistry, Vol. 41, No. 12, 2002 3205

Du et al.
Scheme 2
Figure 2. Structure of [2-ButCtCH-2,2-(CO)2-3-NMe3-closo-2,1-
MoCB10H10] (6) showing the crystallographic labeling scheme. Selected
internuclear distances (Å) and angles (deg): Mo-C(3) 1.995(3), Mo-C(2)
2.002(3), Mo-C(4) 2.044(3), Mo-C(5) 2.104(2), Mo-B(5) 2.357(3), Mo-
C(1) 2.385(2), Mo-B(4) 2.396(3), Mo-B(2) 2.416(3), Mo-B(3) 2.431(3),
B(2)-N 1.613(3), C(2)-O(2) 1.138(3), C(3)-O(3) 1.139(3), C(4)-C(5)
1.291(4); C(3)-Mo-C(4) 116.35(10), C(2)-Mo-C(4) 98.78(10), C(3)-
Mo-C(5) 81.19(10), C(2)-Mo-C(5) 87.17(10), C(4)-Mo-C(5) 36.22(10),
C(4)-Mo-C(1) 87.96(9), C(5)-Mo-C(1) 123.81(9), C(4)-Mo-B(2)
104.10(10), C(5)-Mo-B(2) 126.06(9), N-B(2)-C(1) 122.4(2), N-B(2)-
B(7) 117.8(2), N-B(2)-B(6) 114.1(2), N-B(2)-B(3) 125.3(2), N-B(2)-
Mo 109.64(14), C(5)-C(4)-Mo 74.4(2), C(4)-C(5)-C(6) 140.9(2), C(4)-
C(5)-Mo 69.3(2), C(6)-C(5)-Mo 149.8(2).
in keeping with the anticipated asymmetry of the cluster.
Here again, one signal in each spectrum remains a singlet
upon retention of proton coupling and is relatively deshield-
ed, resonating in the range δ 9.4-12.6. These are attributed
to the boron vertices carrying an NMe3 group. In the 1H and
13C{1H} NMR spectra for 4-6, peaks due the NMe3 unit
are also observed, confirming that this group is retained in
the products. Moreover, broad resonances diagnostic for the
cage CH groups are seen at δ(1H) 1.63 (4), 2.70 (5), and
4.38 (6), and at δ (13C) 56.2 (4), 54.7 (5), and 57.6 (6).12
The significant deshielding of the cage CH proton resonance
in the alkyne complex 6, compared with 4 and 5, is consistent
with the corresponding parameters for analogous anionic
species based on the [nido-7-CB10H11]3- carborane ligand.11
Single crystals of compound 6 were analyzed by X-ray
diffraction methods, revealing the structure shown in Figure
2. The data were of sufficient quality unambiguously to
establish that the NMe3 group is attached to a cage-boron
center C-N-B mechanism for transfer of the NMe3 moiety
rather than the amine’s ability to displace a THF molecule,
otherwise a species having both CNMe3 and BO(CH2)4
groups in the molybdenum-ligating CBBBB ring would form.
To explore their chemistry more fully, derivatives of 1
and 2 were sought. When the reaction that gave 1 was
repeated using [Mo(CO)3(NCMe)2(PPh3)] instead of
[Mo(CO)3(NCMe)3], it was anticipated that [N(PPh3)2][2-
Br-2,2-(CO)2-2-PPh3-3-NMe3-closo-2,1-MoCB10H10], a prod-
uct analogous to 1, might be obtained. However, the only
product isolated after chromatographic workup was the
known molybdenum complex [N(PPh3)2][2,2,2-(CO)3-2-
PPh3-closo-2,1-MoCB10H11] (3),11 identified spectroscopi-
cally. It is not possible to say whether a B-NMe3 species
analogous to 1 is formed and subsequently decomposes, or
if this reaction follows a different route whereby the NMe3
unit is simply lost.
Treatment of compound 1 with Tl[PF6] and ligands L
results in TlBr elimination and formation of the neutral,
zwitterionic complexes [2,2,2-(CO)3-2-L-3-NMe3-closo-2,1-
MoCB10H10] for L ) PPh3 (4) or CNBut (5) and the species
[2-ButCtCH-2,2-(CO)2-3-NMe3-closo-2,1-MoCB10H10] (6)
when L ) ButCtCH. Data characterizing compounds 4-6
are given in Tables 1 and 2. For all three products, the
11B{1H} NMR spectra show 10 resonances (some coincide),
atom in an R position in the CBBBB face of the carborane
ligand. Thus, the site of NMe3 substitution in all of the
foregoing species 1, 2, and 4-6 is reasonably assigned as
being the 3-position. The carborane moiety in 6 is structurally
very similar to that in 1, the B(2)-N distance (1.613(3) Å)
being essentially identical with the corresponding parameter
in 1. Two carbonyl ligands are also terminally bonded to
molybdenum in a normal fashion. The final element of
the molybdenum coordination sphere is the alkyne group
ButCtCH, whose contact-carbon atoms are bonded to the
metal center at distances Mo-C(4) 2.044(3) and Mo-C(5)
(11) Ellis, D. D.; Franken, A.; Jelliss, P. A.; Stone, F. G. A.; Yu, P.-Y.
Organometallics 2000, 19, 1993.
(12) Brew, S. A.; Stone, F. G. A. AdV. Organomet. Chem. 1993, 35, 135.
3206 Inorganic Chemistry, Vol. 41, No. 12, 2002

Cage-Carbon to Cage-Boron NMe3 Transfer
ably be assumed that it is this boron atom which formerly
carried the NMe3 substituent. Thus, the molybdenum atom
is η5-coordinated on one side by an 8-Br-nido-7-CB10H10
carborane group and on the other by a bromide and four
CNBut ligands. The Mo-Br(1) distance, 2.6873(7) Å, is
rather shorter than in 1 and is consistent with the higher
molybdenum oxidation state in 7. This bromide is sited trans
to the centroid of the CBBBB carborane face, with Br(1)-
Mo-centroid 178.8°. The Mo-centroid distance, 1.902 Å, is
somewhat longer than that (1.877 Å) in [2,2,2,2-(CNBut)4-
2-I-closo-2,1-MoCB10H11];10 likewise, the average Mo-
(CNBut) separation in 7 is ∼2.126 Å, perceptibly longer than
in this analogue, where the corresponding parameter is
∼2.111 Å. These two species otherwise have very similar
architectures.
The NMR parameters for compounds 7 and 8 are mutually
very similar and, moreover, closely resemble the correspond-
ing data for the related MoIV species [2,2,2,2-(CNBut)4-2-
Figure 3. Structure of [2,2,2,2-(CNBut)4-2,3-Br2-closo-2,1-MoCB10H10]
(7) showing the crystallographic labeling scheme. Selected internuclear
distances (Å) and angles (deg): Mo-B(3) 2.368(5), Mo-B(4) 2.392(5),
Mo-B(2) 2.408(5), Mo-B(5) 2.462(5), Mo-C(1) 2.469(5), Mo-Br(1)
2.6873(7), B(2)-Br(2) 2.003(5); B(2)-Mo-Br(1) 142.34(13), C(1)-Mo-
Br(1) 143.81(12), C(1)-B(2)-Br(2) 121.3(3), B(7)-B(2)-Br(2) 113.7(3),
B(6)-B(2)-Br(2) 107.4(3), B(3)-B(2)-Br(2) 130.4(3).
1
X-closo-2,1-MoCB10H11] (X ) Br, I).10 In both the H and
13C{1H} NMR spectra of 7 and 8, signals for an NMe3 group
1
are clearly absent. The H NMR spectra show a broad
resonance for the cage CH unit at δ 2.42 (7) and 2.28 (8) of
relative intensity 1, and a sharp signal at δ 1.52 of relative
intensity 36 that corresponds to the four But groups. In the
13C{1H} NMR spectra, the cage-carbons resonate at δ 62.2
(7) and 62.7 (8), respectively. The expected patterns of
resonances for the isocyanide ligands’ three types of C atom
environments are also seen in typical positions, with the
contact carbon atoms of these groups seen as broad,
unresolved triplets at δ 152.0 (7) and 149.1 (8). Compounds
7 and 8, likewise, both have similar 11B{1H} NMR spectra,
with the only significant difference between the two sets of
data being the chemical shift of that boron atom bearing the
halogen. For 7, the substituted boron atom resonates at δ
10.1 and for 8 at δ -5.7. This difference in shielding of
∼15 ppm for bromide versus iodide substituents is very
typical.14 Indeed, this fact in conjunction with the micro-
analytical data serves to confirm the identity of the halogens
present in compound 8.
Whereas the anion [2,2,2,2-(CO)4-closo-2,1-MoCB10H11]-
with I2 and CNBut undergoes metal oxidation, as mentioned
previously, the same anion reacts with I2 and thioethers L
to give cage-substituted products [2,2,2-(CO)3-2,3-µ-I-n-L-
closo-2,1-MoCB10H9] (n ) 7, 11) and [2,2,2-(CO)3-2-I-3,11-
L2-closo-2,1-MoCB10H9].10 As the former of these two
product types contains a novel iodide bridge between
molybdenum and a cage-boron atom, and given that the anion
of 2 already contains a molybdenum-bound iodide, it was
clearly of interest to investigate whether similar reactivity
occurs with compound 2. Because compound 1 is converted
to 2 by treatment with I2, to avoid unnecessary complications,
compound 2 alone was chosen as substrate here. Thus,
treatment of a CH2Cl2 solution of 2 with I2 and 1,4-dithiane
gave a product which initial NMR analysis showed to contain
both the NMe3 feature and a dithiane group. A single-crystal
2.104(2) Å and which has an internal C(4)-C(5) distance
of 1.291(4) Å. In accord with the alkyne ligand acting
formally as a four-electron donor, in the 13C{1H} NMR
spectrum, the ligated carbon atoms resonate at δ 175.0 and
223.3.13 In the related molybdenum complex [N(PPh3)2][2-
ButCtCH-2,2-(CO)2-closo-2,1-MoCB10H11], the contact car-
bons of the alkyne resonate at δ 164.4 and 196.4,11 also in
the range for a four-electron donor alkyne. To our knowledge,
compound 6 is the first structurally characterized metal-
alkyne complex in metal-monocarbollide chemistry.
We have previously shown that the MoII complexes
[2,2,2,2-(CO)4-closo-2,1-MoCB10H11]- and [1,2-µ-NHBut-
2,2,2-(CO)3-closo-2,1-MoCB10H10]-, upon treatment with
I2 and CNBut, are oxidized to MoIV species [2,2,2,2-
(CNBut)4-2-I-closo-2,1-MoCB10H11]10 and [1,2-µ-NHBut-
2,2,2-(CNBut)3-2-I-closo-2,1-MoCB10H10],6 respectively. Given
the relationship of 1 to the two described MoII anions, it
was of interest to examine the reactivity of 1 under similar
conditions. Accordingly, CH2Cl2 solutions of compound 1
were treated with both Br2 and I2 in the presence of CNBut.
Simplistically, it was expected that the product obtained
might be of general formulation [2,2,2-(CNBut)3-2-X-2-Y-
3-NMe3-closo-2,1-MoCB10H10] (X, Y ) Br or I). In practice,
however, the boron-bound NMe3 unit is lost in the reaction,
and the products isolated are [2,2,2,2-(CNBut)4-2-Br-3-X-
closo-2,1-MoCB10H10] (X ) Br (7), I (8)).
The two products 7 and 8 were fully characterized by the
data presented in Tables 1 and 2. Compound 7 was
additionally studied by X-ray diffraction methods, which
established the structure shown (Figure 3). This determination
reveals that a bromine atom is attached to an R boron atom
in the five-membered CBBBB ring that is bonded to
molybdenum, with B(2)-Br(2) 2.003(5) Å. It may reason-
(14) Sprecher, R. F.; Aufderheide, B. E.; Luther, G. W. III; Carter, J. C. J.
Am. Chem. Soc. 1974, 96, 4404.
(13) Templeton, J. L. AdV. Organomet. Chem. 1989, 29, 1.
Inorganic Chemistry, Vol. 41, No. 12, 2002 3207

Du et al.
Spectroscopic data characterizing compound 9 are given
in Tables 1 and 2. The 1H and 13C{1H} NMR spectra confirm
the presence of both NMe3 and cyclo-1,4-S2(CH2)4 groups.
1
A singlet at δ 3.09 (of relative intensity 9) in the H NMR
spectrum and a peak at δ 58.1 in the 13C{1H} NMR spectrum
are assigned to the amine methyl groups. Several multiplets
1
in the range δ ∼3.9-2.8 in the H NMR spectrum are
attributed to the dithiane methylene protons, with four
corresponding resonances between δ 42.3 and 26.6 in the
13C{1H} NMR spectrum. In the 11B{1H} NMR spectrum,
10 resonances are seen (some are coincident), in keeping
with the cluster asymmetry. Of these, two remain singlets
in a fully coupled 11B NMR spectrum, at δ 7.7 and -6.6,
and are assigned to the boron atoms bearing the NMe3 and
thioether substituents, respectively.
Figure 4. Structure of [2,2,2-(CO)3-2-I-3-NMe3-6-{cyclo-1,4-S2(CH2)4}-
closo-2,1-MoCB10H9] (9) showing the crystallographic labeling scheme.
Selected internuclear distances (Å) and angles (deg): Mo-B(5) 2.353(11),
Mo-B(4) 2.354(10), Mo-B(3) 2.387(10), Mo-C(1) 2.404(9), Mo-B(2)
2.452(11), Mo-I 2.8703(11), B(2)-N 1.629(13), B(5)-S(1) 1.924(10);
B(5)-Mo-I 94.0(3), C(1)-Mo-I 81.6(2), B(2)-Mo-I 107.3(3), N-B(2)-
C(1) 123.2(8), N-B(2)-B(3) 127.3(8), N-B(2)-Mo 116.8(6), C(1)-
B(5)-S(1) 123.8(7), B(4)-B(5)-S(1) 124.8(7), S(1)-B(5)-Mo 108.6(5).
Although compounds 1 and 2 were themselves character-
ized, and had their identity well supported by the preparation
and characterization of several derivatives, the precise nature
of their presumed precursor [1-NMe3-2,2,2-(CO)3-closo-2,1-
MoCB10H10]2- remains unclear. Nevertheless, the existence
of the dianionic molybdenum complex is reasonable on the
basis of other known metallacarboranes synthesized from
[7-NMe3-nido-7-CB10H10]2-, for example, [1-NMe3-2,2-
(CNBut)2-closo-2,1-PdCB10H10], characterized by X-ray dif-
fraction.16 Indeed, although the carborane dianion [7-NMe3-
nido-7-CB10H10]2- has not itself been isolated, that it retains
the C-NMe3 linkage during its formation is adequately
demonstrated by the observation that oxidative closure of
this carborane gives 2-NMe3-closo-2-CB10H10, in which the
amine moiety remains bonded to the cage-carbon atom.2c,17
Several unsuccessful attempts were made to identify
[1-NMe3-2,2,2-(CO)3-closo-2,1-MoCB10H10]2- indirectly by
making derivatives. An endeavor was made to prepare the
neutral complex [2,2,2,2-(CO)4-1-NMe3-closo-2,1-MoCB10H10]
by oxidizing CO-saturated solutions of the dianion [2,2,2-
(CO)3-1-NMe3-closo-2,1-MoCB10H10]2- with [Fe(η5-C5H5)2]-
[BF4], but this was unsuccessful. Earlier we have shown11
that addition of HBF4 to CO-saturated solutions containing
the species [2,2,2-(CO)3-closo-2,1-MoCB10H11]3- affords the
monoanion [2,2,2,2-(CO)4-closo-2,1-MoCB10H11]-. How-
ever, similar treatment of [1-NMe3-2,2,2-(CO)3-closo-2,1-
MoCB10H10]2- led only to decomposition.
It was also hoped that addition of suitable cationic metal-
ligand fragments to solutions of [1-NMe3-2,2,2-(CO)3-closo-
2,1-MoCB10H10]2- would yield bimetallic complexes in
which the cationic metal group would be bound to the cage
by exopolyhedral B-HFM bonds.18 If successful, this would
produce a species with a uninegative charge and perhaps
increase stability. However, no isolable products were
obtained from several experiments of this type. Nevertheless,
when the salt [Rh(NCMe)3(η5-C5Me5)][BF4]2 was added to
the described molybdenacarborane dianion in 1:1 molar ratio,
a product was isolated which 1H NMR spectroscopy revealed
X-ray diffraction study established that the product was
[2,2,2-(CO)3-2-I-3-NMe3-6-{cyclo-1,4-S2(CH2)4}-closo-2,1-
MoCB10H9] (9). Retention of the cage NMe3 group in this
reaction presents an interesting contrast with the formation
of 7 and 8.
A perspective view of a molecule of 9 is shown in Figure
4. The complex is seen to consist of an {Mo(CO)3I} fragment
that is η5-coordinated to an 8-NMe3-11-{cyclo-1,4-S2(CH2)4}-
nido-7-CB10H9 carborane ligand. Both the amine and the
thioether substituents are bonded to boron atoms that are in
R positions with respect to the cage-carbon atom in the
CBBBB face that ligates molybdenum. The B(2)-N and
B(5)-S(1) distances, 1.629(13) and 1.924(10) Å, respec-
tively, are unremarkable. Likewise, the Mo-I separation,
2.8703(11) Å, is quite typical.
Compound 9 may be considered formally to be doubly
zwitterionic and as such may be compared with the
closely related compounds [2,2,2-(CO)3-2-I-3,11-L2-closo-
2,1-MoCB10H9] (L ) thioether or ether)10 alluded to earlier.
In these latter species, however, the substituents are at R
and â sites of the carborane CBBBB belt. Their sequential
formation,10 via a â-monosubstituted cluster complex, con-
trasts with the formation of 9 from R-monosubstituted 1. We
have observed that when metals are pentahapto coordinated
by nido-7-CB10H11 cages, those B-H vertices which are at
â sites in the metal ligated CBBBB ring are activated toward
substitution via hydride abstraction (by Me+, H+, etc.)9,11,15
or via oxidation (by I2).10 It may be that in metal-coordinated
n-L-nido-7-CB10H10 carboranes (L ) two-electron donor, n
) 8 or 9), the R B-H vertices in the CBBBB ring are
activated to a second substitution regardless of whether L
is attached at an R (n ) 8, as here) or a â (n ) 9)10 boron
site.
(16) Carroll, W. E.; Green, M.; Stone, F. G. A.; Welch, A. J. J. Chem.
Soc., Dalton Trans. 1975, 2263.
(17) Morris, J. H.; Henderson, K. W.; Ol’shevskaya, V. A. J. Chem. Soc.,
Dalton Trans. 1998, 1951.
(15) Du, S.; Franken, A.; Jelliss, P. A.; Kautz, J. A.; Stone, F. G. A.; Yu,
(18) Ellis, D. D.; Franken, A.; Jelliss, P. A.; Kautz, J. A.; Stone, F. G. A.;
Yu, P.-Y. J. Chem. Soc., Dalton Trans. 2000, 2509.
P.-Y. J. Chem. Soc., Dalton Trans. 2001, 1846.
3208 Inorganic Chemistry, Vol. 41, No. 12, 2002

Cage-Carbon to Cage-Boron NMe3 Transfer
Rh(1)-Mo(1) 2.8294(6), and Rh(2)-Mo(1) 2.7809(5) Å; the
corresponding Rh-Rh distance in the tungsten species is
rather longer, at 2.859(1) Å. However, in the latter case, the
connectivity is hydride bridged, whereas in 10, a carbonyl
ligand bridges the two rhodium atoms. This carbonyl bridge
is somewhat asymmetric, with Rh(2)-C(5) (1.965(4) Å)
being shorter than Rh(1)-C(5) (2.113(4) Å). Three further
carbonyl ligands are bonded to the molybdenum vertex, of
which two are approximately linear (Mo(1)-C(2)-O(2) is
179.2(4)°; Mo(1)-C(3)-O(3) is 177.8(4)°), while the third
is slightly bent (Mo(1)-C(4)-O(4) is 162.4(3)°). This last
carbonyl has partial bridging character, with a long interac-
tion to Rh(2) (Rh(2)‚‚‚C(4) 2.477(4) Å). A similar situation
was observed in the related tungsten species mentioned
previously.
Compound 10 may be viewed as being formed via a redox
process. The molybdenum(0) center in the precursor is
oxidized to molybdenum(+II), with two corresponding one-
electron reductions of each of the rhodium centers from +III
to +II. This is comparable with the process whereby
compounds 1 and 2 are synthesized. However, in the case
of 10, the NMe3 group is lost during the reaction. Notably,
one boron vertex loses a hydride in forming the direct B-Rh
σ linkage, while the cage-carbon atom formally gains a
hydride after the NMe3 group is lost. Whether it is the same
hydride that is involved in both steps can only be speculated.
Physical and spectroscopic data for compound 10 are given
in Tables 1 and 2. In its 11B{1H} NMR spectrum, 10 separate
resonances are seen, in keeping with the molecular asym-
metry. The boron atom that is σ-bonded to rhodium resonates
at δ 56.7, while the adjacent boron vertex involved in the
B-HFRh linkage gives rise to a signal at δ 29.3. Upon
retention of proton coupling, the latter peak is split into a
doublet with J(HB) ) 70 Hz. All of these parameters are
quite typical for these features in such systems.12 In the
related rhodium-molybdenum and -tungsten dicarbollide
species alluded to previously, the σ-bonded boron resonates
at δ(11B) ∼35-45, and that of the agostic-type linkage, at
δ(11B) ∼20-25, with corresponding coupling constant J(HB)
Figure 5. Structure of one of the crystallographically independent
molecules of [2,2,2-(CO)3-7-µ-H-2,7,11-{Rh2(µ-CO)(η5-C5Me5)2}-closo-
2,1-MoCB10H9] (10) showing the crystallographic labeling scheme. Selected
internuclear distances (Å) and angles (deg): Mo(1)-C(2) 2.016(4), Mo(1)-
C(3) 2.027(5), Mo(1)-C(4) 2.029(4), Mo(1)-B(3) 2.253(4), Mo(1)-B(4)
2.286(4), Mo(1)-B(2) 2.329(4), Mo(1)-C(1) 2.378(4), Mo(1)-B(5)
2.379(4), Mo(1)-Rh(2) 2.7809(5), Mo(1)-Rh(1) 2.8294(6), Rh(1)-C(5)
2.113(4), Rh(1)-B(4) 2.317(4), B(4)-H(4) 1.25(4), H(4)-Rh(1) 1.60(4),
Rh(1)-Rh(2) 2.7975(6), Rh(2)-C(5) 1.965(4), Rh(2)-B(3) 2.124(4),
Rh(2)-C(4) 2.477(4); B(4)-H(4)-Rh(1) 108(3), Rh(2)-Mo(1)-Rh(1)
59.81(2), Rh(2)-Rh(1)-Mo(1) 59.232(11), C(4)-Rh(2)-Mo(1) 44.95(9),
Mo(1)-Rh(2)-Rh(1) 60.957(14), Rh(2)-B(3)-Mo(1) 78.82(14), Mo(1)-
B(4)-Rh(1) 75.84(13), O(4)-C(4)-Mo(1) 162.4(3), O(4)-C(4)-Rh(2)
120.6(3), O(5)-C(5)-Rh(2) 142.1(4), O(5)-C(5)-Rh(1) 131.2(3), Rh(2)-
C(5)-Rh(1) 86.6(2).
contained two different pentamethylcyclopentadienyl moi-
eties. Accordingly, adjustment of the reactant stoichiometry
to 2:1 (Rh/Mo) afforded in reasonable yield a brown trimetal
species identified as [2,2,2-(CO)3-7-µ-H-2,7,11-{Rh2(µ-CO)-
(η5-C5Me5)2}-closo-2,1-MoCB10H9] (10).
The detailed architecture of compound 10 was established
by an X-ray diffraction study. The molecule has the structure
shown in Figure 5. Two crystallographically independent
molecules of 10 are found in each asymmetric fraction of
the unit cell. The two are almost identical, and therefore,
only one is discussed here. Compound 10 has consider-
able similarity to the dicarbollide derivatives [1,2-R2-3,3,3-
(CO)3-8-µ-H-3,4,8-{Rh2(µ-H)(η5-C5Me5)2}-closo-3,1,2-
MC2B9H7] (M ) Mo, W; R ) H, Me), which are formed
from [1,2-R2-3,3,3-(CO)3-closo-3,1,2-MC2B9H9]2- via a par-
allel synthetic approach, and for which the compound with
M ) W and R ) Me was the subject of X-ray diffraction
analysis.19 In the present compound, the dirhodium fragment
{Rh2(µ-CO)(η5-C5Me5)2} is bonded to two cluster boron
atoms and to the molybdenum center. One rhodium-to-boron
interaction is a direct sigma bond, with Rh(2)-B(3) 2.124(4)
Å, while the other is a B-HFRh agostic-type linkage, with
Rh(1)-B(4) 2.317(4), Rh(1)-H(4) 1.60(4), and B(4)-H(4)
1.25(4) Å. These two Rh-B distances are similar to the
corresponding values (2.11(2) and 2.39(2) Å, respectively)
in the previous tungsten dicarbollide species. Within the
triangle of metal atoms, distances are Rh(1)-Rh(2) 2.7975(6),
1
also ∼70 Hz.19 In the H NMR spectrum of 10, the agostic
proton is observed as a very broad resonance at rather high
field, δ ca. -14, for which no additional coupling informa-
tion could be resolved. The cage CH proton gives rise to a
broad singlet at δ 1.71, while the two C5Me5 units are seen
as singlets at δ 1.76 and 1.79. These two units also show
characteristic resonances in the 13C{1H} NMR spectrum, with
their contact carbon atoms giving rise to a pair of doublets
at δ 106.0 (J(RhC) 4 Hz) and 108.4 (J(RhC) 6 Hz). The
cage-carbon atom resonates at δ 44.0, while the three
molybdenum-bound carbonyl ligands are seen at typical
positions of δ 221.5, 225.1, and 251.1. Of these, the one at
highest frequency is assigned as the carbonyl with partial
bridging character to rhodium.
Conclusion
The formation of the molybdenacarborane anions in 1 and
2 from their precursor [2,2,2-(CO)3-1-NMe3-closo-2,1-
MoCB10H10]2- appears to occur via a process that involves
(19) Mullica, D. F.; Sappenfield, E. L.; Stone, F. G. A.; Woollam, S. F. J.
Chem. Soc., Dalton Trans. 1993, 3559.
Inorganic Chemistry, Vol. 41, No. 12, 2002 3209

Du et al.
The residue was taken up in the minimum volume of CH2Cl2 (∼5
mL), filtered through a Celite pad, and applied to the top of a
chromatography column. Elution with CH2Cl2 gave a yellow
fraction that was identified by infrared and multinuclear NMR
spectroscopy as the previously reported species [N(PPh3)2][2,2,2-
(CO)3-2-PPh3-closo-2,1-MoCB10H11]11 (3) (0.35 g, 8%).
both a metal oxidation and an oxidative substitution of a
cluster B-H bond, the latter resulting in a transfer of the
trimethylamine moiety from the cage-carbon atom to an
adjacent boron vertex. Compounds 1 and 2 undergo typical
reactions of molybdenacarboranes. The metal-bound halide
may be replaced by donor ligands to give neutral, zwitterionic
species. With CNBut and bromine or iodine, the MoII center
is oxidized to MoIV, with concomitant replacement of
B-NMe3 by B-halide; whereas, by contrast, with iodine
and a thioether, a cluster B-H bond is oxidized and replaced
by B-thioether.
Synthesis of [2,2,2-(CO)3-2-L-3-NMe3-closo-2,1-MoCB10H10]
(L ) PPh3, CNBut) and [2,2-(CO)2-2-ButCtCH-3-NMe3-closo-
2,1-MoCB10H10]. (i) A mixture of compound 1 (0.20 g, 0.20 mmol),
PPh3 (0.08 g, 0.31 mmol), and Tl[PF6] (0.076 g, 0.22 mmol) was
stirred in CH2Cl2 (15 mL) for 12 h. After filtration through a Celite
pad, solvent was removed in vacuo and the residue taken up in
CH2Cl2 (∼2 mL) and transferred to a chromatography column.
Elution with CH2Cl2-petroleum ether (3:1) gave a yellow frac-
tion which, upon evaporation of solvent in vacuo, yielded
yellow microcrystals of [2,2,2-(CO)3-2-PPh3-3-NMe3-closo-2,1-
MoCB10H10] (4) (0.081 g). 31P{1H} NMR: δ 53.2.
Experimental Section
General Considerations. All reactions were carried out under
an atmosphere of dry, oxygen-free nitrogen using Schlenk line
techniques. Some subsequent manipulations were performed in the
air, where indicated. Solvents were distilled from appropriate drying
agents under nitrogen prior to use. Petroleum ether refers to that
fraction of boiling point 40-60 °C. Chromatography columns
(typically ∼15 cm in length and ∼2 cm in diameter) were packed
with silica gel (Acros, 60-200 mesh). NMR spectra were recorded
at the following frequencies: 1H 360.1, 13C 90.6, 31P 145.8, and
(ii) By a similar procedure, using CNBut (23 µL, 0.017 g, 0.20
mmol) in place of PPh3, yellow microcrystals of [2-CNBut-2,2,2-
(CO)3-3-NMe3-closo-2,1-MoCB10H10] (5) (0.064 g) were obtained.
(iii) Similarly, reaction of 1 with Tl[PF6] in the presence of
ButCtCH (70 µL, 0.047 g, 0.57 mmol) afforded purple micro-
crystalline [2-ButCtCH-2,2-(CO)2-3-NMe3-closo-2,1-MoCB10H10]
(6) (0.075 g).
Synthesis of [2,2,2,2-(CNBut)4-2-Br-3-X-closo-2,1-MoCB10H10]
(X ) Br, I). (i) To a CH2Cl2 (40 mL) solution of 1 (0.40 g, 0.40
mmol) was added CNBut (0.19 mL, 0.14 g, 1.68 mmol) followed
by Br2 (0.065 g, 0.41 mmol). The solution was stirred for 2 h, and
the solvent was allowed to evaporate in air. The residue was taken
up in CH2Cl2 (∼2 mL) and chromatographed. Elution with
CH2Cl2-petroleum ether (2:1), followed by evaporation of the
solvent in air, gave orange microcrystals of [2,2,2,2-(CNBut)4-2,3-
Br2-closo-2,1-MoCB10H10] (7) (0.123 g).
20
11B 115.5 MHz. The compounds 7-NMe3-nido-7-CB10H12 and
[{Rh(µ-Cl)Cl(η5-C5Me5)}2]21 were obtained by literature methods;
[Mo(CO)3(NCMe)2(PPh3)]22 was prepared in situ and used without
isolation. All other reagents were used as received.
Synthesis of [N(PPh3)2][2,2,2-(CO)3-2-X-3-NMe3-closo-2,1-
MoCB10H10] (X ) Br, I). (i) The compound 7-NMe3-nido-7-
CB10H12 (0.73 g, 3.82 mmol) was suspended in THF (20 mL), the
mixture was cooled to about -40 °C, and BunLi (3.1 mL, 7.75
mmol, 2.5 M solution in hexanes) was added. The resulting
suspension was warmed to -10 °C, and a solution of [Mo(CO)3-
(NCMe)3] (prepared in situ from [Mo(CO)6] (1.00 g, 3.79 mmol)
refluxed in NCMe (20 mL)) was added by cannula. After warming
to room temperature and stirring for 1 h, a dark red solution was
obtained which was treated with CH2dCHCH2Br (0.46 g, 3.80
mmol). The resultant mixture was stirred overnight, and [N(PPh3)2]-
Cl (2.18 g, 3.80 mmol) was added. After stirring for a further 3 h,
the mixture was filtered and the filtrate slowly evaporated in air to
give ∼1.1 g of dark red crystals. The crystals were washed with
ice-cold acetone (3 × 20 mL) and dried in vacuo, to give pure
[N(PPh3)2][2-Br-2,2,2-(CO)3-3-NMe3-closo-2,1-MoCB10H10] (1) (1.02
g).
(ii) Similarly, reaction of 1 (0.10 g, 0.10 mmol) with CNBut (45
µL, 0.033 g, 0.40 mmol) and I2 (0.026 g, 0.10 mmol) yielded orange
microcrystalline [2,2,2,2-(CNBut)4-2-Br-3-I-closo-2,1-MoCB10H10]
(8) (0.033 g).
Synthesis of [2,2,2-(CO)3-2-I-3-NMe3-6-{cyclo-1,4-S2(CH2)4}-
closo-2,1-MoCB10H9]. Iodine (0.074 g, 0.29 mmol) was added to
a mixture of compound 2 (0.30 g, 0.29 mmol) and 1,4-dithiane
(0.035 g, 0.29 mmol) in CH2Cl2 (20 mL). The mixture was stirred
for 12 h, and then solvent was removed in vacuo. The residue was
redissolved in the minimum amount of CH2Cl2 (∼2 mL) and
chromatographed. Elution with CH2Cl2-petroleum ether (3:1)
removed a red fraction which, upon evaporation of solvent in vacuo
and crystallization from CH2Cl2-petroleum ether, yielded red
crystals of [2,2,2-(CO)3-2-I-3-NMe3-6-{cyclo-1,4-S2(CH2)4}-closo-
2,1-MoCB10H9] (9) (0.084 g).
(ii) Compound 2 was prepared similarly, using I2 (0.97 g, 3.82
mmol) as oxidizing agent in place of CH2dCHCH2Br. Following
purification by column chromatography, with CH2Cl2 as eluant,
[N(PPh3)2][2,2,2-(CO)3-2-I-3-NMe3-closo-2,1-MoCB10H10] (2) (0.51
g) was isolated as a dark red powder.
Synthesis of [2,2,2-(CO)3-7-µ-H-2,7,11-{Rh2(µ-CO)(η5-C5Me5)2}-
closo-2,1-MoCB10H9]. The carborane 7-NMe3-nido-7-CB10H12
(0.24 g, 1.25 mmol) was suspended in THF (30 mL) at ca. -40
°C, and BunLi (1.0 mL, 2.5 mmol) was added. The suspension was
stirred and warmed to ca. -10 °C before solid [Mo(CO)4-
(piperidine)2] (0.47 g, 1.24 mmol) was added. After stirring for 2
h at room temperature, a filtered solution of [Rh(NCMe)3(η5-
C5Me5)][BF4]2 (prepared in situ from [{Rh(µ-Cl)Cl(η5-C5Me5)}2]
(0.80 g, 1.3 mmol) and Ag[BF4] (1.0 g, 5.14 mmol) in NCMe (10
mL)) was added to the reaction mixture by syringe. The resultant
mixture was stirred for a further 2 h. Solvent was removed in vacuo
and the residue chromatographed. Elution with CH2Cl2-petroleum
ether (3:2) gave a brown fraction from which solvent was removed
in vacuo. Crystallization from CH2Cl2-petroleum ether yielded dark
Attempted Preparation of [N(PPh3)2][2-Br-2,2-(CO)2-2-PPh3-
3-NMe3-closo-2,1-MoCB10H10]. Following a procedure similar to
that by which compound 1 was formed, a suspension of 7-NMe3-
nido-7-CB10H12 (0.73 g, 3.82 mmol) in THF (20 mL) was treated
with BunLi (3.1 mL, 7.75 mmol), followed by an NCMe (20 mL)
solution of [Mo(CO)3(NCMe)2(PPh3)] (3.80 mmol). After 1 h,
CH2dCHCH2Br (0.46 g, 3.80 mmol) was added and the mixture
stirred overnight. Thereafter, [N(PPh3)2]Cl (2.18 g, 3.80 mmol) was
added. The mixture was stirred 3 h and then evaporated in vacuo.
(20) Plesek, J.; Jel´ınek, T.; Drda´kova´, E.; Herma´nek, S.; St´ıbr, B. Collect.
Czech. Chem. Commun. 1984, 49, 1559.
(21) White, C.; Yates, A.; Maitlis, P. M. Inorg. Synth. 1992, 29, 228.
(22) Fontaine, X. L. R.; Greenwood, N. N.; Kennedy, J. D.; MacKinnon,
P. I.; Macpherson, I. J. Chem. Soc., Dalton Trans. 1987, 2385.
3210 Inorganic Chemistry, Vol. 41, No. 12, 2002

Cage-Carbon to Cage-Boron NMe3 Transfer
Table 3. Crystallographic Data for 1, 6, 7, 9·CH2Cl2 and 10
1
6
7
9‚CH2Cl2
10
formula
fw
C43H49B10BrMoN2O3P2
987.73
C12H29B10MoNO2
423.40
C21H46B10Br2MoN4
718.48
C12H28B10Cl2IMoNO3S2
700.31
C25H40B10MoO4Rh2
814.43
space group
a, Å
b, Å
Cmca
26.998(2)
17.926(2)
18.963(2)
P21/n
P1h
P21/c
12.5499(7)
24.115(3)
P21/n
8.9100(9)
25.796(2)
9.0850(5)
11.0575(9)
12.304(1)
14.726(2)
93.883(9)
103.008(9)
114.451(7)
1747.5(3)
2
20.368(3)
15.829(3)
21.202(4)
c, Å
9.4584(6)
R, deg
â, deg
γ, deg
V, Å3
Z
98.749(6)
111.609(5)
113.713(3)
9177(1)
8
1.444
293
12.80
0.1098, 0.0533
2063.8(3)
4
1.363
173
6.41
0.0566, 0.0235
2661.3(4)
4
1.748
293
20.27
0.1197, 0.0508
6259(2)
8
1.729
173
14.69
0.0864, 0.0350
F
calc, g cm-3
T, K
1.365
293
26.80
0.0893, 0.0419
µ(Mo KR), cm-1
wR2 (all data), R1a
a
2
2
2
Refinement was block full-matrix least-squares on all F2 data: wR2 ) [∑{w(Fo - Fc )2}/∑w(Fo )2]1/2; R1 ) ∑||Fo| - |Fc||/∑|Fo| with Fo > 4σ(Fo).
brown crystals of [2,2,2-(CO)3-7-µ-H-2,7,11-{Rh2(µ-CO)(η5-
C5Me5)2}-closo-2,1-MoCB10H9] (10) (0.20 g).
remaining carbonyl ligand [C(4) and O(4)] along with the Br atom
are disordered across this mirror in general positions (16e), each
refined with one-half occupancy. This disorder is the likely cause
of the unusually short Mo-C(4) and unusually long Mo-Br and
C(4)-O(4) distances determined in this experiment. Unfortunately,
the crystallographically imposed mirror does not correspond to a
true molecular mirror, making the assignment of the cage-carbon
atom from X-ray data ambiguous. In this regard, the location of
this atom was assigned on the basis of NMR spectroscopic
information and by analogy with compound 6. Thus, the cage-
carbon atom and its symmetry related boron atom [B(3)] were
included in disordered general positions (16e), and each refined
with one-half occupancy. The nitrogen atom of the [N(PPh3)2]+
cation was located at Wyckoff position 8e (3/4, -y + 1/2, 3/4) with
full occupancy.
Structure Determinations. Experimental data for compounds
1, 6, 7, 9 and 10 are recorded in Table 3. Diffracted intensities for
1, 6, 7 and 9 were collected on an Enraf-Nonius CAD4 diffrac-
tometer using Mo KR X-radiation (λ ) 0.71073 Å). Final unit cell
dimensions were determined from the setting angles of 25 accurately
centered reflections. Intensity data were corrected for Lorentz and
polarization effects after which numerical (1, 7, and 9) or semi-
empirical (6) absorption corrections based on the measurements of
the various crystal faces or azimuth scans of ψ data, respectively,
were applied.
Low-temperature X-ray intensity data for 10 were collected on
a Siemens SMART CCD area-detector three-circle diffractometer
using Mo KR X-radiation. For four settings of æ, narrow data
“frames” were collected for 0.3° increments of ω. Almost a full
sphere of data was obtained. The substantial redundancy in data
allowed empirical absorption corrections (SADABS)23 to be applied
using multiple measurements of equivalent reflections. The data
frames were integrated using SAINT.23
The structures were solved with conventional direct methods and
refined by full-matrix least-squares on all F2 data using SHELXTL
version 5.03 and SHELXL-97.24,25 All non-hydrogen atoms were
assigned anisotropic displacement parameters. The locations of the
cage carbon atoms were verified by examination of the appropriate
internuclear distances and the magnitudes of their isotropic thermal
displacement parameters. The acetylene hydrogen [H(4a)] in 6 and
the agostic B-HFRh hydrogens [H(4) and H(34)] in 10 were
located in difference Fourier syntheses; their positional parameters
were refined with fixed isotropic thermal parameters [Uiso(H) )
1.2 × Uiso(parent)]. The remaining hydrogen atoms were in-
cluded in calculated positions and allowed to ride on their parent
atoms with fixed isotropic thermal parameters [Uiso(H) ) 1.2 ×
Uiso(parent), or Uiso(H) ) 1.5 × Uiso(C) for methyl hydrogens].
The anionic unit of 1 is bisected by a crystallographic mirror
plane (Wyckoff positions 8f) which contains the Mo atom, two
carbonyl ligands [C(2), O(2), C(3), and O(3)], the nitrogen and
one methyl group of the trimethylamine substituent [N(1) and C(6)],
and several cage boron atoms [B(2), B(8), and B(11)]. The
The coordinating CBBBB face (including the R-substituted Br)
of the carborane cage in 7 was disordered around a pseudo 2-fold
rotation axis which bisects the ring through B(3) and the C(1)-
B(5) bond. The atoms of the major and minor component ring
systems were restrained to equivalent positions, and respective
occupancies were refined in parts to 96.4% and 3.6%. The Br(2A)-
B(2A) distance was fixed at 2.00(2) Å. Also, the methyl groups on
one of the CNBut ligands were disordered by a 63° rotation about
the C(11)-N(10) bond axis. The major and minor components were
refined in parts, including hydrogen atoms, with occupancies of
56.9% and 43.1%, respectively.
Compound 9 cocrystallized with a molecule of dichloromethane
in the asymmetric unit. The solvent molecule was fully ordered
and refined without restraint; hydrogen atoms were included in
calculated positions. Small residual density peaks (<2.0 e Å-3) near
the positions of the heavy metal atoms in the final difference map
of compound 10 indicate an inability to completely correct for X-ray
absorption effects on poorly formed, irregularly shaped crystals.
Acknowledgment. We thank the Robert A. Welch
Foundation for support (Grant AA-1201) and Dr. John C.
Jeffery, Bristol University, United Kingdom, for assistance
with the structure determination of 10.
Supporting Information Available: Full details of the crystal
structure analyses in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
(23) Siemens X-ray Instruments, Madison, WI, 1997.
(24) SHELXTL, version 5.03; Bruker AXS: Madison, WI, 1995.
(25) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
IC020091W
Inorganic Chemistry, Vol. 41, No. 12, 2002 3211